1. Field of the Invention
This invention relates to a novel method for the production of perfluoroalkyl halogenides (iodides and bromides). More particularly, this invention relates to a method for economically and advantageously producing perfluoroalkyl halogenides useful as intermediates for the synthesis of fluorine-containing products such as, for example, surfactants, agricultural pesticides, and medicines in high yields from readily available raw materials.
2. Prior Art Statement
In recent years, iodine-containing perfluoro compounds have been attracting attention as intermediates and raw materials for the synthesis of various fluorine-containing products. They have found extensive utility as intermediates for the synthesis of surfactants, agricultural pesticides, and medicines, for example. Bromine-containing perfluoro compounds have found extensive utility for the synthesis of similar products and as Halon type anti-inflammatory agents and X-ray shielding agents.
The conventional methods for the production of perfluoroalkyl iodides may be broadly divided into those of the type using perfluorocarboxylic acid derivatives as raw materials and those of the type using fluorine-containing olefins as raw materials. The methods of the former type include a method which comprises heating the silver salt of a perfluorocarboxylic acid and iodine ["Journal of Chemical Society", page 584 (1951)], a method which comprises causing a perfluoroalkanoyl chloride to react with potassium iodide ["Journal of Organic Chemistry", Vol. 23, page 2016 (1958)], a method which comprises causing an alkali metal salt of a perfluorocarboxylic acid to react with iodine in a polar solvent ["Journal of Organic Chemistry", Vol. 32, page 833 (1967)] or in a nonpolar solvent (Japanese Patent Public Disclosure SHO 63(1988)-159336), and a method which comprises causing a perfluorocarboxylic acid to react with iodine in the presence of a peroxide ["Asahi Glass Research Report", Vol. 32, page 117 (1982)], for example.
The methods of the latter type include a method which comprises subjecting a mixture of a fluorine-containing olefin with iodine and iodinepentafluoride to thermal reaction ["Journal of Chemical Society", page 3779 (1961)], a method which comprises causing a fluorine-containing olefin to react with iodine in the presence of potassium fluoride as a catalyst in a polar solvent ["Journal of Organic Chemistry", Vol. 27, page 1813 (1962)], and a method which comprises causing a fluorine-containing olefin to react with iodine in the presence of silver fluoride as a catalyst in a polar solvent ["Journal of Organometallic Chemistry", Vol. 57, page 423 (1973)], for example.
While the methods of the latter type using perfluoroolefins (having at least three carbon atoms) necessarily produce secondary or tertiary perfluoroalkyl iodides, the methods of the former type have an advantage in that desired perfluoroalkyl iodides can be produced by using corresponding perfluorocarboxylic acids as raw materials. The conventional methods using perfluorocarboxylic acids as raw materials, however, entail a disadvantage in that they are highly inconvenient for commercial operation because they necessitate use of a dangerous peroxide or conversion of a perfluorocarboxylic acid into an acid chloride or a metallic salt in preparation for the actual reaction.
The methods heretofore known for the production of perfluoroalkyl bromides include those using perfluorocarboxylic acids as raw materials, e.g. a method which comprises heating a silver salt of a perfluorocarboxylic acid and bromine in a sealed tube ["Journal of American Chemical Society", Vol. 73, page 4016 (1951) and Vol. 74, pages 848-849 (1952)] and a method which comprises causing a perfluorocarboxylic anhydride to react with bromine in a carbon-lined tube filled with activated carbon (U.S. Pat. Nos. 2,647,933; 2,704,776).
The methods using perfluorocarboxylic acids as raw materials, however, have a disadvantage in that they are highly inconvenient for commercial operation because they necessitate a complicated step of converting a perfluorocarboxylic acid into a metal salt or an acid anhydride in preparation for the reaction.
Still other methods heretofore proposed include a method which comprises causing perfluoroalkylsulfur pentafluoride to react with bromine at an elevated temperature of about 500.degree. C. in an alumina tube containing nickel chips (U.S. Pat. No. 3,456,024) and a method which comprises causing perfluoroalkyl iodide to react with bromine in the presence of a peroxide (Japanese Patent Public Disclosure SHO 60(1985)-184033 and SHO 61(1986)-233637), for example.
Perfluorocarboxylic acid fluorides are easily produced by electrolytic fluorination of carboxylic acid chloride or oligomerization of perfluoropropene oxide and tetrafluoroethylene oxide, for example. When perfluorocarboxylic acid fluorides are used as raw materials for the production of perfluoroalkyl halogenides via fluorine-containing carboxylic acid derivatives, this production can be performed by a simplified process and accordingly proves to be highly advantageous.